Pulley/bearing diagnosis

[JHZR2]

I’m making this a separate thread solely for the discussion of pillows to help folks with diagnosis.

On my ML320 I didn’t realize that there are two idlers!

So I have one replacement. It’s OK, I can do the other one sometime, not a huge deal.

But which one is the worst one? One doesn’t spin nearly as much, more so than the new pulley, but not as much or as loud. It spins smooth though. No issues. I assume it has more grease?

The other spins easily and beautifully. I assume it’s because the bearings are still great but there’s no excess grease?

My logic is to replace the one that spins easily, since the other spins smooth. The other I’ll order and replace later.

Please let me know and let’s discuss. But the intention is for this to be a thread about general diagnosis, not my specific vehicle. I think this is universally useful.



Thanks!

 

[Kira]

They spin differently, you say. Are they designed the same way? Maybe they should spin identically?

"...thread about general diagnosis", you say.

What mileage is the vehicle at now? Are you at a maintenance 'milestone'?
Was something making noise? Why was the belt off?

You have access now....do both now. <<This is one thing many generalists would say.
These idlers are not expensive parts to start with, so do not buy cheap ones. <<This is another thing generalists would say.

 

[JHZR2]

They spin differently, you say. Are they designed the same way? Maybe they should spin identically?

"...thread about general diagnosis", you say.

What mileage is the vehicle at now? Are you at a maintenance 'milestone'?
Was something making noise? Why was the belt off?

You have access now....do both now. <<This is one thing many generalists would say.
These idlers are not expensive parts to start with, so do not buy cheap ones. <<This is another thing generalists would say.

Please read the discussion.

I wasn’t clear that they’re identical parts. Same part number, same size. Age unknown. We are diagnosing them based upon the ability to spin freely and the noise.

As noted, there’s another thread about my belt issues. That matter could be discussed in the other thread, so it is separate from this general diagnosis discussion.

This thread is for two identical bearings on two identical pulleys, which one is in better shape?

 

[RooflessVW]

It is my experience that a new, good, healthy bearing will not spin completely freely but smoothly.

 

[D60]

To me smooth and spins free means it's very well broken in but little fear of failure anytime soon.

I personally use SOUND a lot -- if it spins freely and sounds like skateboard wheels, I figure it's VERY dry and the next progression is metal eating metal.

Judging objectively with other people's money, I want to have a credible belief it's near end-of-life. Just spinning free is not enough for me unless there's slop I can FEEL or sounds I don't like I can HEAR.

Otherwise this seems too easily abused as an upsell.

And I'm afraid of an off-the-shelf O'Reilly bearing failing before a well-used OEM bearing. IOW don't fix what ain't broke

 

[JHZR2]

It is my experience that a new, good, healthy bearing will not spin completely freely but smoothly.

So that’s the top one. Spins freely but smooth.

The bottom one has that rattle sound that to me implies that it’s dry.

To me smooth and spins free means it's very well broken in but little fear of failure anytime soon.

I personally use SOUND a lot -- if it spins freely and sounds like skateboard wheels, I figure it's VERY dry and the next progression is metal eating metal.

Judging objectively with other people's money, I want to have a credible belief it's near end-of-life. Just spinning free is not enough for me unless there's slop I can FEEL or sounds I don't like I can HEAR.

Otherwise this seems too easily abused as an upsell.

And I'm afraid of an off-the-shelf O'Reilly bearing failing before a well-used OEM bearing. IOW don't fix what ain't broke

Well in this case it’s two $11.87 INA German made OE idlers. Exactly the same. At 200k and not knowing when they were done, both will be done.

I don’t know what skateboard wheels sound like. The bottom one spins faster/longer and is noisier. More rattle. The top one spins smooth and no noise at all.

Question is which is in better condition.

 

[Kira]

The better one is likely the top one or it could be indeterminate.

 

[JHZR2]

The better one is likely the top one or it could be indeterminate.

Thanks. I suspect it can be, lol. Watch it fails on me before I replace it!

 

[Trav]

So that’s the top one. Spins freely but smooth.

The bottom one has that rattle sound that to me implies that it’s dry.



Well in this case it’s two $11.87 INA German made OE idlers. Exactly the same. At 200k and not knowing when they were done, both will be done.

I don’t know what skateboard wheels sound like. The bottom one spins faster/longer and is noisier. More rattle. The top one spins smooth and no noise at all.

Question is which is in better condition.

Rattling is not a good sign with any bearing. Time to put it in file 13 (aka the bin)

 

[SC Maintenance]

Bearings are not supposed to rattle. I would guess that one. When you turn it by hand do you feel any rough spots? How about axial play?

Any noise tends to indicate they have a rough spot or are dry.

I would replace both anyway - but that my diagnosis.

 

[eljefino]

Does the bearing press out of the pulley? This gives you lots of options if it's a standard size, though I'm confident you'll think the OE design is the best.

There are fascinating varities of a standard bearing, like a 6203, with regard to seals, grease, dust seals, side loading, if you want to geek out, even if you want to just figure out the compromises in your original unit. With differences in seals and other manufacturing methods, some bearings will always have a little more drag.

 

[JHZR2]

Bearings are not supposed to rattle. I would guess that one. When you turn it by hand do you feel any rough spots? How about axial play?

Any noise tends to indicate they have a rough spot or are dry.

I would replace both anyway - but that my diagnosis.

No rough spots. Maybe a tiny bit of axial play or shake.

It will spin for a very long time.

Rattling is not a good sign with any bearing. Time to put it in file 13 (aka the bin)

That’s the one I swapped (bottom).

Does the bearing press out of the pulley? This gives you lots of options if it's a standard size, though I'm confident you'll think the OE design is the best.

There are fascinating varities of a standard bearing, like a 6203, with regard to seals, grease, dust seals, side loading, if you want to geek out, even if you want to just figure out the compromises in your original unit. With differences in seals and other manufacturing methods, some bearings will always have a little more drag.

I suppose they’re servicable, but for less than $12 for the OE German part, might as well swap.